Several metabolic systems in Streptococcus mutans were examined using genetic and molecular techniques. A second transport system for glucose was identified. Using mutants defective in glucose phosphotransferase activity (PTS), we were able to demonstrate that glucose transport and metabolism can occur in the absence of PTS activity. Analysis of this second glucose transport system using metabolic inhibitors revealed that it was driven by a proton motive force. The genes for lactose enzymes in S. mutans and S. lactis were examined by heterologous transformation into a lactose-negative recipient strain of S. sanguis. Analysis of transformants revealed that the genes that code for lactose PTS and phospho-beta-galactosidase activity are located together on the chromosome in S. mutans but present on a plasmid in S. lactis.